docs: perf testing complete + tsys3 datanet fix + Kuma DNS aliases

Perf testing results (#413):
- Host-to-host datanet: all 7 hosts at ~900-940 Mbps (1Gbps line rate)
- Guest-to-guest: all k8s nodes at ~920-1040 Mbps over VLAN 1000
- Storage I/O: NFS writes 27-65 MB/s (spinning disk), reads cached

Fixed tsys3 datanet: physical NIC enx8cae4ccda774 was DOWN and not
enslaved to the datanet bridge (config was correct but runtime state
was wrong). Enslaved manually, verified connectivity.

Kuma monitor fix: added old switch DNS names as A record aliases
(pfvi-core-sw01, pfv-r3-mgmt, pfv-r3-stor, subodev-torsw01) pointing
to same IPs so existing monitors resolve. Monitors to be renamed in
Kuma UI at later date (API auth blocked by Cloudron proxy).

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

WORKING.md

@@ -6,3 +6,6 @@ A commit is blocked while any task below remains unchecked.
 ## Current Tasks
 
 - [x] Switch rename Phase 4-5: mapping.txt + conman/ser2net/udev + repo files
+- [x] End-to-end perf testing (#413): host-to-host, storage, guest-to-guest
+- [x] Fix tsys3 datanet (physical NIC not enslaved to bridge)
+- [x] Kuma monitor fix (DNS aliases for old switch names)